OK, so the EMAV PRU (Electric Motors and Vehicle Company Power Regeneration Unit) isn’t expected to go on sale until sometime next year, but it’s one curious approach to the “range anxiety” problem that caused GM to develop the Volt as a range-extended EV rather than a pure battery-only EV. The PRU takes a simple concept, a trailer that can both store goods and generate 25kWh of electricity from a 750cc diesel engine in order to extend range, and makes it considerably more complicated than it needs to be. For one thing, it’s self-propelled, necessitating on-board lithium-ion batteries, as well as an electric drive unit.

As a result, the projected pricetag comes to a prohibitive $15,000, and the weight reaches an EV range-sapping 1,220 lbs. And for all that, wouldn’t a $15k hatchback make a better “range extender” than this cumbersome trailer? On the other hand, a trailer like this just might work as a rental item, offering a portable generator as well as range extension that its makers say will work with any electric car. But would something like this be more appealing as a simplified, lighter unit (non-self-propelled), or will add-on range extension always struggle to offer more for money than having a gas car as a compliment to an electric car? Given that American families typically have several cars anyway, the answer would appear to be yes… [via GM-volt.com]

Let’s start with Honda Generator is 6500W, which produces 27A at 240V. That’s perfectly compatible with the Leaf’s Level 2 charging (240V <30A). The Generator itself is $3k, and a cheap trailer with an extension cord can be fabbed for $1k to $2k, for a total price of under $5k. The problem is that Level 2 charging takes 8 hours! So you can go 70-100 miles, but then you have to stop for 6 or 7 hours while the Leaf recharges. Not really practical.

So let's now look at what it *really* takes to put the Leaf in to ER CS mode…

According to Nissan, a Leaf driving at 55 mph has a 70 mile range, so it exhausts the battery in 1.25 hours.

That means, you need a generator which can fully charge the Leaf in an hour or so.

To do that, the Leaf will require a rolling Level 3 charger (charges 80% in 30 minutes, per Nissan). Full charge is probably an hour to taper up the last 20%. The problem is that a Level 3 charger is 480V / 125A!

Also: "Nissan warns that if fast charging is the primary way of recharging, then the normal and gradual battery capacity loss is about 10 percent more than regular 220 volt charging over a 10 year period." Not good.

Level3 charging is more power than it takes to sustain cruising speed so it is overkill for a range extender. You won’t be able to put a normal generator on the trailer because they aren’t certified emissions-wise to be an engine that runs while moving over a public road (whatever the EPA calls that). Best / worst case scenario will be if they are regulated like motorcycles (i.e. barely) and you can get a trailer with a hayabusa engine and velocity stacks poking through the lid. On the bright side, maybe some new companies will be able to use this market to develop low cost, light weight exhaust treatment systems.

Buying the combination of Leaf + ER trailer, you’re paying more than the Volt, but getting a less-sophisticated ER system that requires more space, more axles, more weight, and more overall complexity.

Anybody who’d buy one of these would do better to simply buy a Volt.

Of course, if somebody could simplify the ER trailer and get the price down under $5k, then that’d be a very different proposition which might make sense for some larger number of people. In that case, you’d save a little money, and only carry the generator for those rare times when you think you’ll actually needed. The problem is that, as above, if you’re trailering an ER bolt-on any appreciable amount of time, then it’d be a lot easier to get a Volt and be done.

In the end, it appears that GM did a pretty good job with the integrated generator / series-parallel hybrid system for the $8k premium you pay over the Leaf.

When I was an undergrad engineering student I recall volunteering to help out on some senior-level design projects, one of which was called the Hybrid Electric vehicle team (this was 98/99 time frame). They competed in national competitions sponsored by PNGV or DoE or something like that. They were trying to outfit a Chevy Lumina with a series hybrid Hydrogen fuel cell, but the cell stacks were late due to manufacturing delays and the fact that this team wasn’t the only group waiting on one.

They ended up getting around the cell stack delay by building the car as a pure electric vehicle. I don’t recall if they were using lead-acid or NiMH batteries, but the car didn’t get very high range. So they cannibalized their prior-year Lumina series hybrid and used it’s 3cyl Metro engine (that ran on CNG) and put it on a small utility trailer with it’s propane tank to recharge the batteries. After competition the department would host tailgates at the football games using the range-extender trailer and gas tank to run their grill. As I recall, the trailer didn’t weigh more than 400-500 lbs even with the grill on it.

Utterly insane.
Most EVs will be purchased by multi-car households, so you simply use the gas car for long trips, not hook up your $15000 long range trailer.
Even if you are one car household and you occasionally need a long distance trip. RENT a CAR!, Swap with a friend who would probably love to try an EV.
This is a completely loony solution to a problem that doesn’t exist in reality.

I have a great idea: How about we take the electric car, shrink it down, and supplement it with a gasoline-powered engine. Then we could just use the electrical bits to start the car, the rely on internal combustion to take us 300-500 miles before stopping, and we’d have the ability to refuel at tens of thousands of locations? I think that’s where electric car evolution is going.

i think the point of the “self propelled” trailer was to reduce the rolling resistance and load placed on the electric motor. I could see Nissan over engineering a portable power station so that it wont inhibit the joy of driving an EV

I have a trailer that weighs around that amount when loaded, and I know that fuel consumption increases by about 50% when I have it in tow. So, this will increase the energy usage of whatever powertrain you choose, by probably around the same amount. Better to just chuck the whole thing and just drive a regular small car. FAIL …

This brings up the interesting possibility of circumventing the EPA / CARB emission rules. The trailer isn’t part of the car, so it’s not subject to the emission testing program. I doubt if that diesel engine they chose is fully compliant with US EPA Tier 2 bin 5 the way the diesel engine in, say, a regular VW Golf TDI is …

I know somebody who actually built their own range extender for their EV and tested it. He found the same thing, the increased load (aerodynamic drag was, well, a real drag) of towing the trailer hardly made the small bit of net power from the generator even worth having.

We’d be better off having high-capacity charging stations, or developing quick-change battery packs (could drop out the bottom, pull into battery station, lift comes up, lowers empty pack, raises up charged pack, you swipe your card, and you’re back on the road), I think the first of these ideas is more likely to happen than the second.

And don’t poo-poo the FWD front clip pusher concept, it has been done by many, usually using a diesel VW rabbit: http://www.mrsharkey.com/pusher.htm